DL-Ethionine, the ethyl analog of methionine, is known to be a specific liver carcinogen in rats and mice. A cell line derived from rat liver (established in the Nutrition and Metabolism Section of this Laboratory) and tumorigenically transformed by exposure of the cells in culture to DL-ethionine serves as a model for the study of different parameters in the course of chemical transformation. Special emphasis is directed towards the investigation of morphologically definable transformation features; i.e., phenotypic changes, as these are as yet not well understood in epithelial cells. In a preliminary investigation, characterization of the cell lines (nontransformed and ethionine-transformed) has been achieved and, by using cytological and histochemical methods, evidence has been presented for 1) the epithelial nature of these cells (presence of junctional complexes and prekeratin); 2) their origin from liver epithelium (presence of glycogen and G-6-Pase) and 3) the identification of cellular alterations in nucleus and cytoplasm that resulted specifically from ethionine treatment and subsequent transformation. For the understanding of genetically stable modfications in morphology due to transformation, cytoskeletal arrangements and adhesion characteristics of the transformed cells are now compared to those of the nontransformed controls using immunocytochemistry, reflection contrast and phase contrast microscopy, and electron microscopy. Results obtained thus far indicate, in cultures of transformed cells, a loss of cell-cell adhesion via intermediate junctions which appears to be compensated by an increase in cell-substrate adhesion via focal contacts. Concomitantly, the transformed cells exhibit an increase in fibronectin, further suggesting enhanced cell-substrate adhesion. The changed adhesion patterns in the transformed cell cultures may be defined as progressive deficiencies in cell contact interactions.